In many fields, particularly the agricultural chemical field, it is highly desirable to produce compositions which provide a controlled release of an active ingredient. Such compositions can provide desirable control of pests with less frequent and/or lower application rates of pesticides as the active ingredient will be released over a period of time.
Among the approaches taken in the past to provide such controlled release has been the incorporation of the active ingredient into a microcapsule. In the past, such microcapsules have typically been composed of organic polymers such as polyureas. However, due to the presence of polyisocyanates in the core material, such polyurea technology may not be useful with many pesticides (See U.S. Patent Application Publication No. 2008/0254082). Moreover, the use of such organic polymers may not be desirable in some circumstances from an environmental perspective.
In order to overcome these limitations, it has been proposed to encapsulate pesticides in a silica shell employing a sol gel emulsion polymerization process. Thus, for example, U.S. Patent Application Publication No. 2008/0254082 discloses the use of silica microencapsulated pesticides to achieve controlled release such that extended residual activity is observed. Somewhat similarly, U.S. Pat. No. 6,303,149, U.S. Patent Application Publication No. 2007/0292676 and U.S. Patent Application Publication No. 2008/0199523 all disclose sol gel processes for the encapsulation of active ingredients (including pesticides) in non-modified silica shells.
Although such silica microcapsules provide a degree of sustained release, it would be desirable to produce compositions which provide enhanced residual activity, and yet which maintain the benefits of such silica microcapsules.
PCT Application WO 03/066209 discloses an encapsulation process and composition for cosmetic active materials (particularly sunscreens) which can be skin irritants and which therefore should be formulated such that they do not come into contact with the skin. This publication indicates that sol gel produced silica shells can be made more impermeable by post-treatment with a Group IVB, IVA or VA metal alkoxy or acyloxy compound. While such highly impermeable shells are desirable for encapsulating actives which should be maintained within the shell wall, they are not useful for active ingredients—such as pesticides—which must be released from the shells in order to be effective. Accordingly, one would conclude from a reading of WO 03/066209 that post-treating sol gel produced silica shells with a metal would render them too impermeable for use as an effective pesticide encapsulant.